This invention relates to a method and apparatus for destroying unwanted life forms in agricultural soil, particularly soil born pathogens, worms or insects or harmful vegetable life forms, by the application of heat.
Before sowing seeds in plowed earth, it is desirable to destroy unwanted and harmful forms of life, such as soil born pathogens, worms, insects and certain vegetable life forms, which may destroy the seeds or interfere with their proper germination. The practice of such a destruction of unwanted life in agricultural soil, herein briefly called xe2x80x9csoil fumigationxe2x80x9d, has been known for a very long time and various means have been adopted for carrying it out. One of the known means is the application of pesticide chemicals or, in general, chemicals that are able to penetrate into the soil and are active in eliminating the harmful forms of life. However, the use of such chemicals is becoming increasingly difficult and in some cases, must be continuously decreased and will be eliminated in a few years because of international agreements for avoiding ecological damage. Chemicals, in general, may be ecologically damaging. Another known method consists in using steam to penetrate into the soil and kill worms, insects and the like. However, the use of steam is not effective or economical, in view of the very large areas which must be treated. Still another method that has been used in the art is to exploit solar radiation. For this purpose, plastic sheets may be spread on the soil, to be heated by the solar radiation and transmit the heat to the soil. This method, too, is not efficient, nor economical, in view of the very large areas involved, and, anyway, is practical only in some seasons and some locations where the solar radiation is sufficiently intense and cannot be considered, therefore, a generally satisfactory method.
It is therefore a purpose of this invention to provide an efficient method for the soil disinfection and in particular, for the destruction of soil born pathogens, worms and insects and the like, as well as harmful vegetable forms of life.
It is another purpose of this invention to provide such a method which is very effective down to a significant depth into the agricultural soil.
It is a further purpose of this invention to provide such a method that can be applied to areas of any dimension.
It is a still further purpose of the invention to provide such a method which is in no way dependent on climatic conditions or on particular seasons.
It is a still further purpose of the invention to provide such a method which has no economical disadvantages and does not require the introduction into the soil of undesirable chemicals.
It is a still further purpose of this invention to provide an apparatus for carrying out the aforesaid method.
It is a still further purpose of the invention to provide such an apparatus that is simple and not costly to build or to operate.
Other purposes and advantages of the invention will appear as the description proceeds.
The method of the invention is characterized in that flames are generated into the soil, at the desired depth and at predetermined distances between them so as to produce a relatively uniform heating of the soil, and are displaced within the soil along desired trajectories to cover any desired agricultural area.
Preferably, the method is carried out by creating narrow trenches in the soil and advancing the flames along said trenches concurrently with creating the same. Typically, the trenches are narrow clefts created in the soil and particularly in already cultivated soil, which is therefore not compact and easily yields to the creation of clefts or trenches. Preferably, the flames are produced by igniting streams of liquid or gaseous fuel that are continuously fed to the desired depth in the soil. The flow rate of the fuel is determined so as to create in the soil, adjacent to the flame produced by the ignited fuel, a temperature of at least 600xc2x0 C. and preferably between 1000xc2x0 and 1500xc2x0 C. The temperature created in the soil is preferably from 100xc2x0 to 160xc2x0 C. More preferably, the clefts or trenches along which the flames are driven are sufficiently close so that the minimum temperature of the soil at intermediate points between them should not be lower than 120xc2x0 C. Under prevailing conditions, and depending of climatic and seasonal conditions, the amount of heat transmitted to the soil is comprised between 1 million and 1,4 million calories per square meter of soil. The amount of fuel used is calculated, taking into account the nature of the fuel, so as to provide the desired quantity of heat. The speed by which the flames are progressed along the clefts or trenches should be sufficiently low to permit the heat to propagate between neighboring trenches to achieve the desired minimum temperatures of the soil between trenches. The use of the word xe2x80x9ctrenchesxe2x80x9d to determine the clefts of the soil through which the flames are caused to progress should not be construed as limiting in any way the shape or dimensions of the said clefts, which will depend on each individual instance and on the shape and size of the tools used to create them, as well as on the condition of the soil before the trenches are created. They may therefore be vertical with straight sides, or have a V-shaped cross-section and may vary from the shape of sharp clefts to that of furrows, such as created by plows.
The apparatus for carrying out the method of the invention comprises a frame which supports a number of tools for creating the trenches in the soil, which will be called hereinafter xe2x80x9cplowsxe2x80x9d, without in any way intended to limit their shape or dimensions or mechanical structure by the use of this term, and a corresponding number of burners, situated immediately after the plows. The word xe2x80x9cafterxe2x80x9d refers here to the direction of motion which will be imparted to the apparatus and it merely indicates that the burner travels along a trench that is being created and preferably immediately behind the plow that creates it. The apparatus can be supported by wheels and is provided with means for attaching it to a vehicle, preferably a tractor. In an optional form of the invention, the beam supporting the plow and the burners is provided with two foldable wings, so that it may be spread out when in use to cover a greater width than it will occupy when not in use. Further, in a more preferred embodiment of the invention, two supporting beams are provided, one behind the other, and will support plows and burners in such a way that those carried by one beam will create and heat trenches that are situated between the trenches created and heated by the plows and burners supported by the other beam. The beams need not have the same width, and it may be that the apparatus will create trenches that are closer in the center of the treated area than on the sides. It may be that in this case, the apparatus is advanced in successive treatment stages so that in a second stage, trenches will be created intermediate to those created in the first stage, at least at the sides of the treated areas, so as to produce in the end a uniform treatment of the relevant soil area.
The plows which are part of the device may be of any desired type or shape. They are generally shaped similarly to old-fashioned plows, or simply curved cutting blades, as will be illustrated hereinafter; but their shape and size will depend on the condition of the soil that is being treated. If the soil has been plowed before and is therefore already broken up and offers very little resistance to the advances of the plows, these may act essentially as a protection of the burners, allowing them to advance along the soil without having to displace earth and therefore meet with mechanical resistance. However, if the soil is more compact, more robust plows must be provided and it may even be necessary to provide rotary blades, actuated by power that can be derived from the tractor which pulls the device. The burners should be sufficiently narrow or terminate with a sufficiently narrow outlet pipe to advance behind the plows without encountering any significant resistance of the earth. Otherwise, they may be of any desired type, as conventionally available, and need therefore not be described. Fuel tanks can be provided for each burner on the apparatus itself, or may be carried by the tractor or other pulling device, and fuel can be pumped to the burners by any convenient pump means.